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2016-7-15

Research leading detection of low concentrations of gas present in exhaled human breath to health checkups and early detection and treatment of serious diseases is being performed. As gas sensors using nanomaterials can detect various gases even at low concentrations, installing such sensors in electronic healthcare devices is sought after, and research and development are being actively conducted.

Semiconductor gas sensors detect gas through reduced electrical resistance due to gas molecules attached to the surface of crystalline semiconductor materials. For this, gas sensors need a specific surface area of nanomaterials. In order to use nanomaterials for conventional gas sensors, a complicated flow was necessary, from nanomaterials synthesis to cleansing, uniform dispersion of solvent, applying on substrates, and sintering. Thus, there is a concern that manufacturing technology of such gas sensors requires significant time and labor, increasing cost.

A group of researchers led by Assistant Professor SUGAHARA Tohru at The Institute of Scientific and Industrial Research, Osaka University, succeeded in producing nanostructured gas sensor devices for detecting volatile organic compounds (VOC) in breath for the purpose of healthcare in time equivalent to or shorter than one tenth of the time required for manufacturing conventional gas sensors. This group improved conventional complicated production methods, developing a simple production method of just sintering substrates applied with materials. This gas sensor’s sensing response was comparable to the top-of-the-line sensors reported all over the world.

Since demand in healthcare products is on the rise, there is a lot of activity in research and development of sensors for checking health and disease by examining the gas components of a person’s breath. Breathalyzers for finding out who is driving drunk have already been commercialized. Recently, breath sensors for early detection of life-style diseases such as cancer and diabetes have been developed, but most of them are large, bulky and expensive. If gas sensors with high sensitivity are produced thanks to this group’s research results, portable breath sensors enabling early detection of diseases will gain popularity.

Abstract

3D-network of ultra-fine single-crystal α-MoO3 nanorod arrays based gas sensors show a prompt response and discrimination to VOCs. S. Cong, T. Sugahara, and co-workers illustrate the performance of the sensors strongly depend on the specific morphologies of the nanorod arrays, such as length, number and coverage of nanorods in the 3D network. The arrays are spontaneously grown by a simple single-step solution route. A prompt response and obvious discrimination of ethanol, methanol, isopropanol and acetone vapors at 573 K are investigated via the modulation of the resistance of the gas sensors. The conductance modulation of the nanorod arrays are attributed to the hydrogen ions decomposed from VOCs intercalated into the van de Waals’s gaps of layered α-MoO3 and the subsequent reduction the cornered oxygen to H2O. The sensitivity, response time and recovery time of the sensors strongly depend on the specific morphologies of the nanorod arrays, such as length, number and coverage of nanorods in the 3D network. A reaction mechanism in which the 3D-network nanorod arrays adsorb and react with the target molecules more readily than the seed layer is proposed to explain the different response and recovery times of the sensors. These random 3D-network nanorod arrays with functionally tunable morphology are promising for universal application as gas sensors for detecting various vapors, and provide valuable insights for the production of fast, large-scale, low-cost and simple synthesis of sensing devices.

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a. Photo figure of the gas sensor device             b. Cross-sectional FE-SEM image of the MoO3 nanorod arrays.

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To learn more about this research, please view the full research report entitled “Diverse Adsorption/Desorption Abilities Originating from the Nanostructural Morphology of VOC Gas Sensing Devices Based on Molybdenum Trioxide Nanorod Arrays” at this page of the Advanced Materials Interfaces website.


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